Digested products of stabilized fibrin with various proteases are useful as a diagnostic marker in clinical diagnosis. For example, as shown in FIG. 1, plasmin-digested products of stabilized fibrin (cross-linked fibrin), i.e., DD/E monomer as a basic unit, and its polymers (DD/E polymers such as DXD/YY, YXY/DXXD, and DXXY/YXXD) are widely used as a diagnostic marker for disseminated intravascular coagulation (DIC). The plasmin-digested products of stabilized fibrin may be collectively referred to as, for example, D-dimer, D-D dimer, DD/E complex, or cross-linked fibrin degradation products (XDP).
The various proteases can also digest fibrinogen which is present in blood. For example, digested products of fibrinogen such as fragment X, fragment Y, fragment D1, and fragment E3, which contain one or more D domains and E domains in each of their molecules which are the components of D-dimer, may be generated by plasmin. The plasmin-digested products of fibrinogen may be collectively referred to as FgDP.
D-dimer generated by digesting stabilized fibrin with proteases, and digested products of fibrinogen (FgDP) generated by digesting fibrinogen with proteases may often coexist in the blood of a patient with thrombosis. Both digested products are referred to as FDP (see FIG. 1).
Although it was considered that the main component of D-dimer in the plasma of a patient with thrombosis was a DD/E fraction having a molecular weight of about 230 kDa, recently it has known that multimers having higher molecular weights, such as a DXD/YY fraction, a YXY/DXXD fraction, and a DXXY/YXXD fraction, are actually the main components (see non-patent literature 1).
In recent years, underlying diseases which result in death by thrombosis and/or embolism have shown an increasing trend, and a clinical laboratory test for detection of thrombus has been in progress. At an early stage, a measurement of FDP by determining digested products of fibrin/fibrinogen in serum using a polyclonal antibody against fibrinogen (Fbg) has been used for diagnosis of thrombosis. However, this method had a problem that it sometimes showed a falsely high level, due to an insufficient removal of fibrinogen.
In order to solve this problem, a D-dimer reagent which does not react with fibrinogen and can measure only digested products of stabilized fibrin (D-dimer) as DD/E complex in parallel with the measurement of FDP was required.
As a method for measuring D-dimer, for example, a method based on antigen-antibody reaction (i.e., a latex agglutination method or an ELISA method) in which a monoclonal antibody which recognizes D-dimer is immobilized on a solid phase such as latex particles or a plastic plate and D-dimer is bound to the immobilized monoclonal antibody is known (patent literature 1).
However, in this method based on antigen-antibody reaction, a currently-used monoclonal antibody immobilized on the solid phase does not only reacts with D-dimer, but also sometimes reacts with fragment X, fragment Y, fragment D1, and/or fragment E3 which have structures similar to that of D-dimer. When such monoclonal antibodies are used the monoclonal antibody immobilized to the solid phase may be bound to fragments other than D-dimer at the time of measurement, and thus, an inaccurate value is sometimes obtained.
To solve these problems, the following methods are disclosed. In this regard, it could not be said that monoclonal antibodies used in the following reagents were specific for D-dimer. For example, patent literature 2 has reported a D-dimer measuring reagent which reacts with multimers of DD/E fraction and the monomer of DD/E fraction, but does not react with X fraction, Y fraction, D fraction, and E fraction, and has at least 10% of reactivity to DD/E fraction, with respect to the reactivity to the tetramer of DD/E fraction. However, it has been revealed in patent literature 3 that antibody DD-M1653 (deposit No. FERM P-19687) concretely described in patent literature 2 reacts with multimers of DD/E fraction and the monomer of DD/E fraction, and X fraction and Y fraction, but does not react with D fraction and E fraction, and therefore, it cannot be said that this antibody is specific to D-dimer.
Further, patent literature 2 does not show whether or not D-dimer contained in a sample can be specifically and accurately measured. Patent literature 3 discloses that even if a monoclonal antibody having a relatively low specificity to D-dimer is used, the actual amount of D-dimer can be accurately measured using a D-dimer measuring kit consisting of a liquid reagent comprising a monoclonal antibody having a reactivity to D-dimer, and a carrier (or a solution containing the carrier) on which monoclonal antibody having a reactivity to D-dimer is immobilized, but D-dimer contained in a sample cannot be measured easily, specifically, and accurately.
Recently, due to advances in medicine, and advances in treatment and therapeutic drugs, for example, a thrombolytic agent is used to treat a patient with thrombosis. It is considered that fibrinolysis occurs in a fashion that it is unlikely to occur under the physiological environment, as described above, and the presence of digested products of fibrinogen including fragment D has become not to be ignored. Therefore, patent literature 4 discloses that when fragment D is present in a sample, in order to avoid to obtain a measured value lower than the actual value, due to inhibition of agglutination by interference of fragment D to a latex agglutination reaction, i.e., uncertain effects of fragment D derived from the sample, an excess amount of fragment D is previously and artificially added so that D-dimer can be accurately measured. However, D-dimer in a sample cannot be specifically and accurately measured on use of only the intrinsic specificity of an antibody.
As described above, a D-dimer reagent specific to digested products of stabilized fibrin (D-dimer) has been desired, but an antibody capable of specifically and accurately measuring D-dimer using only the intrinsic specificity of a monoclonal antibody, or a reagent comprising such an antibody, has not been reported.
In addition, although the measurement of FDP and D-dimer using a plasma sample has become a commonly-used technique, there has been a problem that FDP and D-dimer rarely shows false high values. Non-patent literature 2 discloses that there is a possibility that FDP and D-dimer shows false high values, when coagulation and/or fibrinolysis are promoted by collecting plasma from a patient.